Motor vehicle crashes are the leading cause of death and a major contributor to non-fatal injury in adolescents 1, 2. Teen drivers' crash risk is especially high in the presence of teen passengers3-6. Peer influences are pervasive, powerful, especially salient during adolescence and associated with health-risk behaviors7, but the variability and mechanisms involved are not well understood8. One factor that may promote risky behavior in adolescence is a possible imbalance in brain development between affective and cognitive control systems8-10, resulting not only in riskier choices overall, but also increased reward activity during risk taking in the presence of peers11, and heightened sensitivity to social rejection12,13. In this investigation, we aim to elucidate neurocognitive predictors of: (1) risky teen driving; (2) susceptibility to peer influence in the context of teen driving; and (3) the ability to overcome risky peer influence. To achieve these aims, we propose to integrate neuroimaging (fMRI) measures into a currently funded study that experimentally manipulates peer influences in a state-of-the-art driving simulator. Main outcomes include behaviors in the simulator that are associated with high rates of injury and fatality in real drivig contexts (a composite of speeding, close following distances, traffic light violations). We hypothesize that: [(1a) increased activity in neural reward systems during a risk- taking task14, and (1b) decreased activity in cognitive control systems during a response inhibition task15, in the fMRI environment will predict higher propensity .toward risky-driving behaviors in the simulator; (2a) increased reward activity during the risk task14, and (2b) increased neural activity in regions associated with distress during exclusion16 in the neuroimaging environment will predict increased susceptibility to risk taking in the presence of peers in the driving simulator; and (3) increased neural activity in cognitive control systems will predict decreased susceptibility to peer influence in the driving simulator], as cognitive control systems could serv to buffer negative affective responses during socially threatening situations, and could also serve to reduce the impact of reward responses induced by taking risks in the presence of peers.11 As such, we hypothesize that [reward and social distress sensitivity, as well as a tendency to recruit cognitive control resources will interact with the social situation to render adolescents differentially susceptible to behaviors that put them at risk for crash in the presence of peers]. Preliminary data collected using key elements of the proposed protocol are consistent with our hypotheses [and suggest that neural measures explain variance in key outcomes that is not explained otherwise]. The proposed research will increase understanding of the mechanisms that lead to variability in risky behavior in adolescents, as well as mechanisms of peer influence and ability to resist such influence. Individual differences in neurocognitive resources may not only interact with the social situation to promote risk, but may also serve to buffer social vulnerability to risk; this work may eventually allow us to develop more effective programs that efficiently reduce risk across multiple domains.